Solid alkaline detergent compositions are widely used for household and industrial dishwashing, laundering clothing and general surface cleansing. The greater amount of such cleaning compositions consumed consists of solid powders, granules, or tablets. These detergent compositions typically incorporate a condensed phosphate hardness sequestering agent and a source of alkalinity such as an alkali metal hydroxide, carbonate, bicarbonate, silicate or mixtures thereof as their primary cleaning components. The hardness sequestering agent acts to condition the wash water by chelating or otherwise complexing the metal cations responsible for the precipitation of alkali metal builder salts and detergents. The alkaline components impart detergency to the compositions by breaking down acidic and proteinacious soils. For heavy duty industrial and institutional washing, highly alkaline chemicals such as the alkali metal hydroxides are commonly incorporated into solid detergent compositions.
In order to be effective for these applications it is necessary that the components of the solid detergent be uniformly distributed throughout the composition and that they dissolve readily in the aqueous washing medium which is employed. Soluble, solid granules incorporating uniformly-dispersed components have been formed by spray-drying aqueous slurries of the detergent components. This method requires expensive equipment such as spray drying towers and consumes large amounts of energy in the drying process. Water-sodium hydroxide slurries can be hardened by externally heating the slurries above the melting point of the sodium hydroxide monohydrate. Besides being energetically disadvantageous, these methods commonly employ temperatures at which sodium tripolyphosphate can wholly or partially revert to the pyrophosphate, orthophosphate or mixtures thereof which are much less effective in sequestering water hardness factors. Attempts to form effective solid detergent compositions by simply blending the components in particulate form often fail to achieve adequate homogenization of the components. Furthermore, solubilization difficulties are often encountered when anhydrous builder salts are combined in this manner. The high temperatures used in the spray-drying or aqueous dispersion processes can degrade other detergent components. Many applications require a source of active halogen in the solid detergent compositions to destain or bleach. The high temperatures necessary to dry and disperse the various components often lead to the total destruction of organic halogen-containing components.
A substantial need exists for methods to prepare homogeneous solid alkaline detergent compositions which rapidly dissolve in aqueous media. A need also exists for methods to prepare water-conditioning and/or active-halogenated solid detergent compositions which avoid phosphate reversion and loss of active halogen.